At present, waste electric wires are separated into copper and coating plastics such as polyethylene (PE), polypropylene (PP), or Polyvinyl Chloride (PVC) and recycled as industrial materials. However, the fine electric wires such as communication cables have not been recycled enough because of the insufficient development of separation technology.
FIG. 1 shows the 2002 statistics of electric wire production in Korea. As shown in FIG. 1, in 2002 the electric wire output and communication cable output in Korea were about 4 trillion won and 5 billion won in the value of production, respectively. Among them, waste electric wires and waste communication cables releases into the environment were about 500 billion won and 100 billion won in value.
If the separation efficiency is low in separating fine copper wires from plastic coatings, the coating plastics cannot be recycled and, therefore, a lot of money is required to completely separate the fine copper wires. The fine electric wires such as communication cables generally consist of copper and plastics such as PE, PP, PVC, etc. Each of them can be recycled after being separated into each material. A large amount of waste electric wires are annually generated from reconstruction and replacement of old communication cables, and due to increase in use of cars and electronic products. To recycle the waste electric wires, it is essential to develop the technologies to completely separate the copper wire and the coating plastics. The coating plastics may not be recycled if the metal such as copper are not removed thoroughly. Thus, the technology to completely remove the metal during a pre-process has to be developed inevitably.
The amount of the plastics used is increasing 10% yearly because of its excellent material properties. It is predicted that the plastics production will reach about 11 million tons within five years and the waste plastic releases into the environment will come up to about 5 million tons within five years. Enormous economic injury as well as environmental problems may be caused if the technology to recycle the coating plastics is not developed. The plastic separation technology will contribute for environmental protection, recycling of useful resources, plastic industry development, and economic development.
Electric wires consist of a conductor part and a coating part. The conductor part is generally made of copper or aluminum. The coating part consists of an insulator to insulate the conductor and an outer coating to protect the insulator and the conductor part from damage. Both the insulator and outer coating are made of PVC, PE, Rubber, etc. Thus, in order to remove copper from the coating of waste electric wires, the insulator and outer coating have to be separated from the conductor.
Several electrostatic separation systems to remove the copper from the plastic coating of waste electric wires have been developed. For example, Korean utility model 288589, Seo, describes an electrolytic electrostatic induction separation system. FIG. 2. is a schematic diagram of the electrolytic electrostatic induction separation system disclosed in the Seo utility model. The electrolytic electrostatic induction separation system includes an electrolyzer consisting of an NA belt (100) charged with negative and a stainless net (200) charged with positive, and a paper belt (300) for electrostatic induction, which moves vertically over the NA belt (100). The NA belt (100) is made of nitrile-butadiene rubber including XE2 (or active carbon dust) of 27˜30%. In the Seo's separation system, the copper bits charged with negative by the NA belt (100) are electrostatic-induced and attracted to the paper belt (300) when the paper belt (300) moves vertically over the NA belt (100). The copper bits separated from the plastic coating bits are collected into a collection container (400) installed below the paper belt (300). The untreated residues are collected into another collection container (500) installed at the rear of the stainless net (200). The plastic coating bits are attached to the surface of the NA belt (100) and, then, collected into a coating collection container (600) by means of a scraper. However, in the Seo's separation system, the paper belt (300) must be replaced after being used for a predetermined period and the simple stainless net (200) structure is difficult to generate optimum electrostatic induction. In addition, the disposition structure of three collection containers fails to achieve complete separation of the plastic coating and copper. Particularly, the Seo's separation system fails to achieve high separation rate of the coating plastics because it passes over the influence of interrelation between positive and negative electrodes, such as the distance between the negative and positive electrodes, the width ratio of the negative electrode to the positive electrode, and the structure of the two electrodes, to the electrostatic induction.
As other examples of conventional separation system, FIG. 3 through FIG. 5 are schematic diagrams of the electrostatic separation devices according to the Korean Utility Model 232140, Jang (FIG. 3), Japanese publication patents JP2001-283661, Tetsuya et al. (FIG. 4), and JP1995-178351, Showa and Norihiro (FIG. 5). The electrostatic separation devices of FIG. 3 and FIG. 5 separate the coating plastics and the metal wire by charging sidewalls of a chamber so that they have an opposite polarity each other and making input materials free falling. These separation devices can separate large particles but is difficult to handle small particles less than 1 mm. In detail, the small particles may clings to the sidewalls by static electricity due to eddy currents which are occurred in the chamber because of the sidewalls with opposite polarity. The electrostatic separation device of FIG. 4 includes a rotating cylinder on which input materials are supplied and a separating container in which the metal wire and the coating plastics are collected separately. However, the separation device of FIG. 4 can accurately separate when the mixing ratio and supply of the input materials are constant. Moreover, the separation device of FIG. 4 cannot improve a selection rate because of the very simple electrode structure.